Large, heavy duty trucks often include a key-slotted input shaft that conveys power from an engine to a non-synchronous transmission. A drive shaft, in turn, conveys the power from the transmission to one or more drive wheels that move the truck over the road. To aide in shifting gears, a conventional clutch typically couples the engine to the input shaft. To smoothen the shift action of the transmission, a clutch pedal in the cabin of the truck can be partially depressed to disengage the conventional clutch. With some trucks, fully depressing the clutch pedal, or pressing a separate pushbutton on the transmission shift lever, engages what is known as a clutch brake. When engaged, a clutch brake slows or stops the rotation of the input shaft, which allows a non-synchronous transmission to be shifted when the engine is rotating while the truck is stationary.
A typical clutch brake is an annular disk with frictional wear-resistance faces. The clutch brake encircles the input shaft and is keyed to it such that the clutch brake can slide along the input shaft in an axial direction. In the rotational direction, however, the keyed connection causes the clutch brake and the input shaft to rotate and stop as a unit. To stop the rotation of the clutch brake and thus stop the rotation of the input shaft, fully depressing the clutch pedal forces an axially movable but rotationally stationary clutch plate against one face of the clutch brake. The axially movable clutch plate is usually part of a throw-out bearing housing mounted between the conventional clutch and the clutch brake. Upon fully depressing the clutch pedal (or depressing an equivalent pushbutton), the clutch brake becomes sandwiched and clamped between the axially movable clutch plate and an opposing stationary clutch plate. The stationary clutch plate is usually between the clutch brake and the transmission and is sometimes referred to as a transmission bearing retainer cap. Frictional force between the clutch brake and the two adjacent clutch plates is what slows or stops the rotation of both the clutch brake and the input shaft.
In examples where the clutch brake is a continuous disk extending circumferentially uninterrupted around input shaft 4, it can be very time consuming to replace a worn or otherwise defective clutch brake. Replacement often involves having to first remove the transmission so that the original clutch brake can be slid axially off one end of the input shaft. Some clutch brakes have a pivotal or separable joint that facilitate replacement without having to remove the transmission. Such clutch brakes, however, are not always provided by the original truck manufacturer, and some separable clutch brakes can be easier to install than to remove.